Simplify the following expression: $k = \dfrac{1}{10q} - \dfrac{7}{4q}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10q$ and $4q$ $\lcm(10q, 4q) = 20q$ $ k = \dfrac{2}{2} \cdot \dfrac{1}{10q} - \dfrac{5}{5} \cdot \dfrac{7}{4q} $ $k = \dfrac{2}{20q} - \dfrac{35}{20q}$ $k = \dfrac{2 -35}{20q}$ $k = \dfrac{-33}{20q}$